The present invention is an improvement over the joint disclosed in U.S. Pat. No. 3,815,940 issued June 11, 1974 to Lawrence F. Luckenbill and assigned to the common assignee, Mueller Co., Decatur, Illinois. In the aforementioned patent, the joint disclosed obviated certain problems in prior "stab" type joints for flareless or smooth end pipe. More particularly the joint in the aforementioned patent had a split gripper ring which was adapted to be contracted tightly about the pipe after the pipe had been stabbed into the body member and when the pipe was subjected to pull-out which moved or tended to move the pipe outwardly of the body member. The initial grip on the pipe by the gripper ring was provided by the particular configuration of the gripper ring and, more specifically, by the configuration of the plurality of axially spaced teeth on the interior cylindrical surface of the gripper ring. In this respect, the annular split gripper ring of the aforementioned patent was provided with a plurality of axially spaced teeth on its interior cylindrical diameter, the teeth being so designed that at least the teeth at or adjacent the ends of the gripper ring always had contact with the exterior of the pipe and initially bit into the pipe upon stabbing of the pipe into the joint. By such an arrangement, there could be no rocking of the gripper ring as would occur in those situations where the gripper ring was molded so as to supposedly have complete engagement of all teeth, but because of manufacturing tolerances resulting during molding, only the intermediate teeth made contact to initially grip the ring, thus, causing the rocking which resulted in slippage when an outward pull was placed on the pipe.
The manufacturing cost for the gripper ring of the type disclosed in the aforementioned patent is high and additionally the quality control in manufacturing must be strictly adhered to. It would be more desirable to manufacture a split gripper ring wherein the design of the teeth was such that upon initial contact, caused by stabbing of the pipe, all teeth would engage the pipe. However, as mentioned above, manufacturing tolerances cannot be controlled this accurately and while some gripper rings made according to this method would be satisfactory, others made from the same molds would not operate satisfactory and consequently the design of gripper rings of the aforementioned patent resulted.
While the joint of the aforementioned patent has proved very satisfactory in most instances of operation, it has been found that problems do exist in such a joint resulting from its design. In the design of the joint of the aforementioned patent, the gripper ring is located against the sealing ring and the relationship between the inside diameter of the body member and the gripper ring's outside diameter is such that there is actually no or little resultant dimensional interference at the time of stabbing of the pipe and therefore the initial gripping is due almost solely to the stiffness of the gripper ring. Since the extent of initial grip is of utmost importance and since the amount of rigidity or stiffness of the gripper ring is limited, the initial grip is set off by a large dimensional interference grip to guarantee against unsatisfactory pull-out strength of the joint.
Additionally difficulties were encountered when using the joint of the aforementioned patent with pipe which was not particularly round at the time of stabbing. For example, polybutylene (PB) pipe becomes normally very out of round from coiling and when such pipe was stabbed into the joint of the type of the aforementioned patent it would sometimes pull out quite easily from the body member. This was caused because the initial grip by the gripper ring was inadequate due to lack of good engagement of its teeth on the out of round pipe. Also another disadvantage of this type of joint was caused by the out of round pipe, in some instances, engaging the sealing ring in a manner to push the sealing ring out from its seat thus ruining the effectiveness of the sealing ring.
Temperature and pressure extremes have affected the sealing characteristics of joints of this type in the past. For example, it has been found that joints of the prior art, even including the joint of the aforementioned patent, are susceptible to air leaks under certain circumstances when low temperatures (below 35.degree. F) and low pressures (generally less than 10 psig) exist. Under normal conditions of temperature and pressure such joints operate satisfactory with no air leaks but when the pipe is flexed and when the joint has been in service for a considerable length of time and the resiliency of the O-ring has decreased from age, the O-ring becomes unseated and is not easily reseated since there is no positive load on the same in addition to the load upon which it is normally subjected by the pressure of the fluid in the system. This results in leaks on the joint.